Re: New public API

["Alexey Parshin" <alexeyp@gmail.com>]

Yeah, that's a pre-requirement. But in that case, returning just const char
* is more appropriate..

2006/2/21, Ilya Volynets <ilya@total-knowledge.com>:
>
> This is one of the options I was thinking about. Only problem is that
> source of the data may not be of the appropriate type.
> Example:
> In Krzyzstov's case, where he embeds his servlet container directly into
> Apache, header values are stored as table of (char*, char*)
> If we retrieve this data and return it
> as std::string we'd have to store it
> somewhere.
>
> -----Original Message-----
> From: "Alexey Parshin" <alexeyp@gmail.com>
> Date: Tue, 21 Feb 2006 11:20:48
> To:"C++ Servlet Engine Discussion" <cppserv@total-knowledge.com>
> Subject: Re: New public API
>
> IMHO, ref counting is bad :( Every time I've used strings with ref
> counting
> it was giving me one problem or another. Of course, it depends on coding
> style..
>
> We can solve that problem partually if we return "const string&".
>
> In that case, if one wants just to use a string w/o altering its content -
> it can be done like this:
>
> const string& myString = myClass.myMethod();
> cout << myString << endl;
>
> Does it make sense to you? This approach is pretty effective.
>
> 2006/2/21, Ilya Volynets <ilya@total-knowledge.com>:
> >
> > 1. Don't know. Maybe yes maybe no
> > In any case - it's probably be bad with gcc.
> > 2. Let's see if we can get reasonable ref counting
> >
> > -----Original Message-----
> > From: Krzysztof Rzymkowski <rzymek@gmail.com>
> > Date: Tue, 21 Feb 2006 00:24:56
> > To:C++ Servlet Engine Discussion <cppserv@total-knowledge.com>
> > Subject: Re: New public API
> >
> > On Mon, 2006-02-20 at 22:37 +0000, Ilya Volynets wrote:
> > > I am aware of retval optimization, though I am not sure about
> semantics
> > in case of C++ - what if copy constructor has side effects?
> > >
> > Are you sure there's a guarantee that a copy constructor will be called
> > when an object is returned by value? I think there's no such guarantee,
> > nor there should be any.
> >
> > > As for optimizations on copy from
> > > The library, I'm not sure again - I
> > > think it's *supposed* to copy in this case, but I don't remember.
> > >
> > > Auto-ptr/ref counting is something I'd prefer, and it's semantically
> > closest to java
> >
> > Now the question is: is allocating heap memory via new is that much
> > faster then copying an object? (Though in case of a big vector is sure
> > is)
> >
> > >
> > > -----Original Message-----
> > > From: Krzysztof Rzymkowski <rzymek@gmail.com>
> > > Date: Mon, 20 Feb 2006 23:15:18
> > > To:C++ Servlet Engine Discussion <cppserv@total-knowledge.com>
> > > Subject: Re: New public API
> > >
> > > On Mon, 2006-02-20 at 11:00 -0800, Ilya A. Volynets-Evenbakh wrote:
> > > > One thing I was thinking about (and even started using in some
> cases)
> > > > is to change methods returing collections. The way it is now:
> > > > virtual std::vector<std::string>  getAttributeNames()
> > > > This means that whole vector, as well as every string inside will be
> > copied
> > > > (possibly twice - inside function when creating retval, and then to
> > the
> > > > actual
> > > > return value). Now, instead we could change signiture as follows:
> > > > virtual void getAttributeNames(std::vector<std::string> &out)
> > > > This will avoid unnessesary copying.
> > > >
> > > > Java does not have to worry about it, since it returns references,
> and
> > thus
> > > > only one copy of object is created.
> > >
> > > It is possible for a STL implementation to user reference counting in
> > > vector's copy constructor, thought the SGI's STL does simple copying.
> > > It is as well possible for the compiler to use return value
> optimization
> > > [1], thought it is not always possible to write the getters in a way
> > > which allows RVO.
> > >
> > > Another option would be to use std::auto_ptr [2] or boost::shared_ptr
> > > [3].
> > >
> > > I would like to keep the API as close to the Java version as it is
> > > possible. So I'd rather stick with option 1 (ignore the problem) or 2
> > > user some sort of reference counting.
> > >
> > > [1] http://cpptips.hyperformix.com/cpptips/ret_val_opt
> > > [2] http://gcc.gnu.org/onlinedocs/libstdc
> > > ++/latest-doxygen/classstd_1_1auto__ptr.html
> > > [3] http://www.boost.org/libs/smart_ptr/shared_ptr.htm
> > --
> >
>
>
>
> --
> Alexey Parshin,
> http://www.sptk.net
>



--
Alexey Parshin,
http://www.sptk.net